Conventionally, a cylinder injection-type internal combustion engine has been put into practical use as an internal combustion engine for an automobile, and use of alcohol-containing fuel including alcohol such as ethanol is considered as fuel for this internal combustion engine. In this case, in the cylinder injection-type internal combustion engine, fuel which has been highly pressurized by a high-pressure pump is stored in a delivery pipe serving as a pressure accumulation pipe, and the high-pressure fuel in this delivery pipe is injected directly into a combustion chamber through a fuel injection valve. As fuel pressure control for the high-pressure pump, there is known a technique for setting a target fuel pressure based on an engine operating state, and for performing fuel pressure feedback control such that actual fuel pressure reaches the target fuel pressure.
In the case of the use of alcohol-containing fuel, alcohol-containing fuel is not easily evaporated compared with gasoline, so that there is concern about reduction in low-temperature starting of the engine. Particularly, a range below the freezing point is physically equal to or lower than the flash point of ethanol, and the engine may not be easily started up. In this regard, there is proposed a technique including a means for setting a starting target fuel pressure based on alcohol concentration of fuel and engine temperature, and a means for prohibiting the fuel injection through the fuel injection valve until a difference between the starting target fuel pressure and an actual fuel pressure becomes a predetermined value or smaller at the time of starting of the internal combustion engine (see, e.g., JP-A-2010-37968). Moreover, in this case, it is proposed that the starting target fuel pressure should be made higher as the alcohol concentration is higher or as the engine temperature is lower.
According to the above-described configuration, the fuel injection is started after increasing the fuel pressure to the starting target fuel pressure at the time of starting of the engine. Furthermore, even though vaporization characteristics of fuel are different according to the alcohol concentration and engine temperature, the starting target fuel pressure suitable for the these alcohol concentration and engine temperature are set to promote the vaporization of injected fuel, thereby improving the low-temperature starting of the engine even in the case of the use of alcohol-containing fuel.
As for fuel pressure control in the case of use of gasoline fuel, generally, after commencement of the starting of the internal combustion engine by a starter, the high-pressure pump is driven with a predetermined discharge amount until a engine rotation speed reaches a predetermined starting determination value (i.e., before completion of starting), and the fuel pressure feedback control is started after the engine rotation speed has reached the starting determination value (i.e., after completion of starting) as a result of first explosion.
During the fuel pressure feedback control by the high-pressure pump, generally, a feedforward term and feedback term are respectively calculated, and a control command value for the high-pressure pump is calculated based on these feedforward term and feedback term. More specifically, the feedforward term is calculated based on a fuel injection amount of the fuel injection valve, and the feedback term is calculated based on a deviation between the target fuel pressure and actual fuel pressure and a predetermined feedback gain. In this case, on the assumption that the fuel pressure feedback control is started after the completion of starting, the feedforward term is calculated based on the fuel injection amount after the completion of starting.
In the case of the use of alcohol-containing fuel, the injection amount is larger than gasoline fuel despite the same required torque of the internal combustion engine, and the fuel pressure is changed greatly due to a periodic start of fuel injection after commencement of the starting of the engine. In addition, if the alcohol concentration of fuel varies, the fuel injection amount differs accordingly, so that the fuel pressure is also changed. For this reason, the fuel pressure feedback control may be started at an early stage so as to limit such a change of fuel pressure.
However, the existing technique assumes a start of the fuel pressure feedback control after the completion of starting the engine, to cause such a defect that the change of fuel pressure at the very beginning of commencement of the starting cannot be limited. Thus, there is concern about inconvenience caused to the starting up of the internal combustion engine.